This invention relates to a process and apparatus for the treatment of crude oils and, more particularly, to the hydrocracking of heavy hydrocarbons in the presence of catalyst to provide useable products and further prepare feedstock for further refining.
As the reserves of conventional crude oils decline, heavy oils must be upgraded to meet world demands. In heavy oil upgrading, heavier materials are converted to lighter fractions and most of the sulfur, nitrogen and metals must be removed. Heavy oils contain a large portion of material boiling above 524° C. (975° F.) or higher. These heavy hydrocarbon feed stocks may be characterized by low reactivity in visbreaking, high coking tendency, poor susceptibility to hydrocracking and difficulties in distillation. Most residual oil feed stocks which are to be upgraded contain some level of asphaltenes which are typically understood to be heptane insoluble and toluene soluble compounds as determined by ASTM D3279 or ASTM D6560. Asphaltenes are high molecular weight compounds which may contain heteroatoms which impart polarity.
Heavy oil must be upgraded in a primary upgrading unit before it can be further processed into useable products. Primary upgrading units known in the art include, but are not restricted to, coking processes, such as delayed or fluidized coking, and hydrogen addition processes such as ebullated bed or slurry hydrocracking (SHC). U.S. Pat. No. 5,755,955 describes a SHC process which has been found to provide high liquid yields with much reduced coke formation through the use of catalyst.
In SHC, a three-phase mixture of heavy hydrocarbon feed cracks in the presence of gaseous hydrogen over solid catalyst to produce lighter products under pressure at an elevated temperature. Iron sulfate has been disclosed as an SHC catalyst, for example, in U.S. Pat. No. 5,755,955. Iron sulfate monohydrate (ISM) is expensive and may not be sufficiently available to catalyze all of the SHC units the world may need to upgrade vast supplies of heavy oil. Other minerals such as bauxite have been shown to be an excellent SHC catalyst for example in U.S. Pat. No. 8,123,933 B2.
U.S. Pat. No. 5,171,727 describes a method for preparing a catalyst which involves introducing a metal and a heteropolyacid into an oil feed. The feed is then heated to form an organometallic compound, which is then converted to a catalyst under hydrocracking conditions. The metal is described as an oxide, sulfide, or salt of a Group IV to Group VIII metal. The heteropolyacid can be phosphomolybdic acid in an amount, expressed as molybdenum, of 0.01 wt % to 2 wt %.
Molybdenum catalyst systems of either oil-soluble molybdenum or a solid molybdenum on carbon matrix, known as carbonized molybdenum, are effective for SHC. However, the cost for molybdenum catalysts are high and strongly dependent on the market price volatility.
Toluene can be used as a solvent to dissolve and separate carbonaceous solids from lighter hydrocarbons in the SHC product. The solids not dissolved by toluene include catalyst and toluene insoluble organic residue (TIOR). TIOR includes coke and mesophase and is heavier and less soluble than asphaltenes. Mesophase formation is a critical reaction constraint in slurry hydrocracking reactions. Mesophase is a semi-crystalline carbonaceous material defined as round, anisotropic particles present in pitch boiling above 524° C. The presence of mesophase can serve as a warning that operating conditions are too severe in an SHC reactor and that coke formation is likely to occur under prevailing conditions.
Due to the anticipated demand for SHC operations to upgrade heavy oil, greater supplies of effective catalyst will become necessarily desirable.